Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Routers, switches, and other device are used for interconnection of networks. Routers will typically exchange routing information packets to share cost, link and/or destination information with one another. Each router then builds its own routing table and forwards packets to other nodes according to its routing table. Usually, the routes with the lowest costs are favored over other routes. In some instances, the costs of routes can be manipulated in order to engineer or control the traffic through the interconnected networks.
Virtual Local Area Networks (VLANs) are a way of tagging traffic within a LAN so that groups of nodes designated as belonging in one VLAN can share the same infrastructure (e.g., switches and links) with nodes belonging in other VLANs, but not be allowed to talk directly to nodes from the other VLANs.
Sometimes it might be desirable for multiple networks (e.g., network “partitions”) to be merged into a single network, but VLAN tags in one partition do not necessarily have the same meaning as VLAN tags in other partitions. Rather than re-configuring all the VLAN numbers of nodes within one of the partitions, a technique may be used whereby the physical nodes that interconnect the partitions (known as the “cut set switches”) perform VLAN mapping. VLAN mapping changes the VLAN number when forwarding traffic between the partitions. Sometimes for a particular VLAN within one of the partitions, a cut set switch might be configured to drop traffic tagged with a particular VLAN number, rather than forwarding it into a different partition.
VLAN mapping may be used in bridges, layer 2 switches, routers, and in routing bridges implementing Transparent Interconnect of Lots of Links (TRILL) —a draft standard within the Internet Engineering Task Force (see RFC 5556 “Transparent Interconnection of Lots of Links (TRILL): Problem and Applicability Statement” May 2009).